(1) Field of the Invention
This invention relates, in general, to a method and apparatus for article transfer from one point to another. More particularly, the invention relates to transport apparatus which has particular utility in combination with silk screen printing apparatus for the silk-screen printing of designs on various articles or ware in a continuous, automatic, stepwise fashion. Even more particularly, it relates to apparatus means, and a method, for rapidly transporting ware such as plastic containers or bottles automatically in stepwise fashion and presenting such to a printer head on a silk-screen printer whereat the ware is printed, and afterwards transporting such ware to a curing station and further downstream.
(2) Description of the Prior Art
The silk-screen printing of various ware such as plastic bottles or containers has been practiced now for several years. In general, such a process involves the continuous transporting of ware, spaced-apart a predetermined distance from one another along a horizontal path. The ware is continuously fed, in step-wise fashion, by a conveyor-like device, through various zones. Initially, it passes through a pre-treatment zone whereat that portion of the ware to be printed is conditioned, e.g., by treatment with a flame. Earlier, prior to the flame treatment, the ware may be passed through a zone whereat the ware is subjected to air treatment to remove any dust particles or other foreign particles from the surface to be printed. Following the flame treatment, the ware passes to a printing zone. At that location, the ware is individually printed with a predetermined design and in a predetermined location, as desired.
An early chain indexing system designed to carry plastic containers in stepwise fashion through various work stations on a screen printing apparatus is disclosed in U.S. Pat. No. 3,315,780. That patent issued on Apr. 25, 1967, and was assigned to the assignee of the present invention.
On all automatic and semi-automatic silk-screen printers, the ware must be lifted up to the screen for printing. This is generally to allow the silk-screen motion, which is back and forth in a horizontal plane, to avoid the ware transporting and supporting hardware. The ware, each piece spaced apart equidistant from one another, travels along a horizontal plane parallel to that of the silk screen motion in a lengthwise direction just below the printing head. The mechanism for lifting each piece of the ware, in stepwise fashion, to the print station generally involves independently driven means for both the lifting of the ware up to the print station and removal of the ware therefrom, back down to the plane of travel. This interrupted motion naturally hinders the production efficiency and, as a result, neither the printer nor the transport system can operate to full potential. Thus, for some years now, this problem has been of concern.
At the speeds of operation desired and which automatic machinery is capable of handling (70 pieces per minute and higher), this usually requires cam actuation. It is desirable to limit the number of cams in operating devices, however, as one or two additional cams in an overall apparatus increases the number of support bearings, interconnecting linkages, etc., and reduces reliability accordingly.
One attempt at addressing the problem is disclosed in U.S. Pat. No. 4,398,627, which issued on Aug. 16, 1983. That patent discloses, according to the patentee, a high productivity device for feeding cylindrical objects to silk screen printing machines. In general, the device comprises, in combination, a transport means and means operatively connected thereto for presenting an object to be printed to a silk-screen printer and then removing that printed object from the printer so that it can be conveyed towards subsequent working stations. The transport means, in general, comprises two vertical longitudinal plates each provided along its length with a plurality of equidistantly spaced-apart notches or seats for receiving the corresponding ends of the objects to be printed. During transport, the objects are first clamped and then moved from one rest position, i.e., opposed set of notches, to another set of notches immediately downstream, arcing in clockwise motion above a center line during transport. At the same time, the longitudinal plates are caused to move in an upstream direction so that the free pair of upstream notches can be loaded with another object. And, then the operation reverses. Thus, the plates and clamping means operate so as to rotatably reciprocate in opposite directions over circumferential arc paths, on opposite sides of a centerline. At the same time that the objects are being moved by respective clamps to the next downstream set of notches, the device for presenting and removing an object from the print screen rotates in a counterclockwise direction to remove an object from the printer and at the same time to pick up an object from the furthest downstream location of the transport means (i.e., the last set of notches) so as to present it to the printer, to be printed. This device comprises a double gripper means located on one arm of the device for removing an object from the printer and a double sucker (i.e., suction cups or "nests") located on another arm of the device for picking up an object from the transport means and presenting it to the silk-screen printer. Thus, this latter device rotates in a counterclockwise arcing direction at the same time that the clamping means on the transport device operate in a clockwise arcing motion. Then, as the clamping means operate in the reciprocal direction, the double gripper means and double sucker operate in a clockwise motion. With such rotatable motion, the suction nests and double gripping means also operate above and below a centerline, parallel to that of the operation of the clamping means and longitudinal plates. Subsequent to the removal from the print zone, the objects are conveyed towards other downstream working stations by, apparently, like transport means, as earlier described.
Although the apparatus disclosed in U.S. Pat. No. 4,398,627 may be found suitable, at least in certain printing applications, its use is believed attendant with certain disadvantages. First of all, it is an extremely complex apparatus and requires numerous tie rods and mechanical linkages. Two sets of clamp bars must arc clockwise above a center line in perfect synchronization with two sets of complex cam operated suction nests operating counterclockwise below another centerline. The accessibility for repair; when needed, or for adjustment and changeover to other size objects seems somewhat limited. And, there are many moving parts that present the potential for injury to the operator or set up person. At high operating speeds, instability is believed likely to be encountered, as the machine can resemble a "thrasher" in its operation.